Celebrating its 80th birthday yesterday, the BBC World Service announced that seven million Iranians now tune in to its broadcasts, a rise of 85 per cent over three years. That's an index both of popular hostility to the Ahmadinejad regime and of the vital role of the World Service in keeping people on both sides informed.

Yesterday, the Service threw open its doors to let its public see and hear its inner workings. Among all the slightly bilious self-congratulation there was the occasional reality check. For the first time ever the morning editorial conference, known as 'the Nine O'Clock', was broadcast live as 40 or so senior editors sat around a table and explained how they saw the news day ahead. The polite consensus was shattered by Africa service editor Josephine Hazeley, who argued that putting Mitt Romney's primary wins at the top of news bulletins gave too much prominence to what was "a local American story." This chimed with feedback from the audience: a colleague admitted that listeners were "bored rigid with American politics."

The discussion highlighted the impossibility of talking to a global audience – yesterday the figure bandied about was 225 million – and giving even a fraction of that number the news they really want to hear. But the journalistic resources are still enviably rich, even after a cull last year that closed seven language services and cost 650 jobs, a quarter of the total. At the Nine O'Clock, the head of the Arabic service noted that he had three correspondents in Syria, in addition to all the UGCs – user-generated content – flooding in. When the conference discusses upcoming events in Syria or Iran, Sri Lanka or Afghanistan, it is with unique authority, thanks to all the local experts around the table.

If a slight mood of ennui emanated from the discussions, perhaps it was just a quiet day. Elections coming up in Russia – "Putin's meeting with the party, there's not much to expect," said the Russia editor, eliciting the comment: "You sold that story really well!" Business: "There's some fatigue over the eurozone crisis, but it goes on and on..." Newshour editor: "It's one of those mornings when there's no obvious lead..." Josephine Hazeley tried to energise the meeting with a story about refugees flooding from the Democratic Republic of Congo into Uganda, but another person around the table later remarked, "Until Josephine mentioned the word 'rape', people's eyes glazed over – but then rape is such a stereotype about the Congo..."

There was also the hint of a tasty little row from the day before still simmering away. After President Sarkozy stated that the French journalist Edith Bouvier had been rescued from Homs, the World Service led on it strongly - only to have to recant half an hour later when Sarkozy changed his tune. "I was always told you don't go on air without two sources," one editor pointed out with a hint of smugness, earning the retort, "We had several million sources for Sarkozy having said that..."

In many places the World Service retains an extraordinary status, and the more troubled the country the more vital its work, which gives correspondents in the field a heavy weight of responsibility for getting things right. This was brought home to me some years ago in Kashmir, when I was this paper's correspondent there. In Srinagar one day, spotting my conspicuous hair and skin, a large and angry demonstration got it into their heads that I was the BBC correspondent, a common mistake everywhere in the subcontinent - and held me responsible for what was regarded as a vile slander in a recent bulletin on the restive state's majority Muslim population. I narrowly escaped being lynched.

For the editors in London responsible for foreign language broadcasts, the local importance of what they do can be a source both of pride and anguish. Josephine Hazeley recalled with pride how during the 10-year civil war in Sierra Leone, her home country, "At 5pm every day the rebels would put their weapons down to listen to my programme, Focus on Africa." But she also recalled her terror when she had to report on air how "the rebels were coming to where my mum lived; I was really shaking."

A veteran reporter for the Sinhala service remembered how his insistence on reporting the news neutrally from the island's civil war led to him and his wife, already ostracised by Tamils, being shunned by the expatriate Sinhalese community. "They don't understand you have to be neutral – they don't want to understand."

The World Service was the child of the British Empire. Celebrating the birthday yesterday, the BBC unblushingly began with a snippet of George V's first Christmas broadcast, written for him by Rudyard Kipling no less, in which he growled to "all my peoples throughout the Empire... to men and women so cut off by the snow, the desert or the sea that only voices out of the air can reach them."

But if it is true that Britain lost an empire and failed to find a role, the imperial legacy that is the World Service remains a precious resource. Within the modern Beeb it may sometimes have seemed the poor, quaint relation across town, but if any vestige of the corporation's original charter remains intact, the World Service is where it is. This is why cuts, and complaints about lack of editorial robustness that have surfaced recently about the Russian service, for example, become the source of bitter argument. What the World Service says matters.

As the Sinhala service correspondent learned to his cost, the crux of the World Service's challenge is to irritate everyone. In the words of Alexander Solzhenitsyn, no less, "The BBC has a special mission to accomplish."

On the airwaves: A history of the World Service

1932 Begins life in December as BBC Empire Service. BBC director-general John Reith announces: "The programmes will neither be very interesting nor very good."

January 1938 Arabic becomes the first foreign-language service.

November 1939 Renamed BBC Overseas Service.

1940 Moves east across central London from Broadcasting House to Bush House in Aldwych after original offices damaged by parachute mine.

1941 Dedicated European service added, becoming a vital resource for those living in Nazi-occupied countries.

1965 "External Services of the BBC" shortened to "BBC World Service."

1985 Goes off air for first time when journalists strike at ban on Sinn Fein programme.